Various techniques have been devised for remotely operating valves. Fluid control lines and electrical wires have long been utilized for transmitting operational signals to remotely positioned valves, thereby significantly reducing the time and expense of achieving valve operation. Numerous automated remote control systems provide feedback from the remote valve to the central station indicative of the operational position of the valve, thereby enhancing computer control and increasing system reliability.
Fluid control conduits or electrical cables are frequently not used, however, for controlling subsurface valves due to the high installation and repair costs for such conduits or cables, poor reliability, and/or governmental regulations. As an alternative, acoustically transmitted signals have been proposed for operating certain remotely positioned valves, including subsurface valves. U.S. Pat. No. 3,902,447 discloses operation of subsea control valves in a mooring system to release compressed air into ballast tanks and thus change bouyancy. U.S. Pat. No. 4,095,421 discloses the use of sonic signals transmitted through water to generate electrical pulses, which then actuate relays to regulate operation of control valves, which in turn control blowout preventers in an offshore oil well. U.S. Pat. No. 4,284,143 briefly discloses the use of acoustic signals for either transmitting control signals to or for transmitting data from a subsurface satellite well. U.S. Pat. No. 4,667,763 teaches transmission of electrical signals, radio signals or acoustic signals to apply power through a relay to a solenoid for controlling a safety valve.
Remote operation of a valve may be accomplished with a pyrotechnic or explosive device. One technique for remotely controlling the release of fluid from an accumulator, for example, employs a pyrotechnic valve. U.S. Pat. No. 4,619,285 discloses a valve which utilizes the explosive gas from a pyrotechnic device located in the valve body to move a piston and thereby free a spool, releasing gas to a normally stowed inflation system. In a similar manner, U.S. Pat. No. 3,900,211 discloses a fast-dump valve for releasing compressed fluid upon command to an inflatable automobile seatbelt. It is also known that pyrotechnic devices may be activated in response to acoustic signals.
Each environment in which a valve is used and the function that valve serves in the overall system define a set of conditions which influence preferred techniques for remotely controlling the valve in that environment. The subsea environment and the control of valves in fluid transmission lines, such as those used for transmitting gas from offshore wells to land-based distribution systems, create unique problems. Conventional fluid control lines, electrical wires, or other conduits between the operator station and the remote underwater valve are often not economically practical. Nevertheless, extremely high reliability is demanded of the technique used to control such valves, since valve operation at critical times effectively regulates the flow of fluid in the pipeline system. Also, each of a plurality of subsea valves in a gas transmission pipeline may rarely require operation, although the system may not allow for occasional testing of the valve operation, so that one cannot effectively determine that a particular valve is no longer operational until after it failed its intended function. This failure could result in a hazardous condition and cause severe economic loss.
Accordingly, most prior art subsea valves in gas transmission pipeline systems are not operated remotely, but rather are manually opened or closed when required. A diver or robot typically is sent subsea to locate the valve, verify its position and thus the function of the valve in the pipeline system, and manually open or close the valve as instructed. Although considerable expense and delays are necessarily associated with this technique, the environment in which the valve is placed and the function of the valve are such that remote control of the valve is generally considered impractical.
A previous system for remotely controlling valves in a subsea gas transmission line utilized acoustic signals for locating and controlling operation of the pipeline ball valves. The system utilized gas pressure in the pipeline as the powering force for operating the ball valve actuator. This previous system has not been widely accepted in the industry, however, in part due to its high cost and concern regarding the reliable operation of the conversion of gas pipeline energy to hydraulic control circuit energy.
The disadvantages of the prior art overcome by the present invention, and improved techniques are hereinafter disclosed for reliably controlling operation of a remote fluid transmission pipeline.